I. Field of the Invention
The present invention generally relates to fertilizer additives and fertilizer compositions and to methods for their preparation and use. More specifically, the present invention is directed to fertilizer additives and compositions including chelated metal ions to provide micronutrients necessary for plant growth.
II. Description of the Background
Agriculturally, metal ions are essential nutrients for plant growth. Soil deficiency because of the unavailability or exhaustion of metal ions is very often the cause of poor plant growth. Crop deficiencies occur at extremely low levels of metal deficiency, i.e., at levels of parts/million in the plant tissue. Both soil and foliar application of chelated metal ions may prevent, correct or minimize crop deficiencies. Chelated complexes have been favored because the chelated metal ions remain soluble in different or changing environments. See Chen and Barak, Advances in Agronomy, vol. 35, pp. 217-239 (1982). Conventional products have used synthetic chelates. However, even though widely accepted as the best method for the administration of metal ions, synthetic chelates are expensive to produce. See, Barak and Chen, Soil Sci. Soc. Am. J., vol. 51, pp. 893-896 (1987). Accordingly, conventional chelated metal additives have been expensive. Therefore, less expensive, yet still efficient, chelating systems have been sought.
The use of citric acid as a chelating agent to provide an inexpensive, naturally occurring alternative has been proposed. However, it was shown that metal chelates of citric acid were unstable at a pH above 7. See, Cline, et al, Soil Sci. Soc. Am. J., vol. 46, pp. 1158-1164 (1982) and U.S. Pat. No. 5,372,626.
Prior methods for the chelation of metal ions for agricultural use also proposed the introduction of inorganic anions to stabilize the pH. However, these anions may have been associated with ecological damage and their addition adds to the expense of the fertilizer.
Accordingly, there has been a long felt, but unfulfilled need for more efficient, more economical and more environmental friendly fertilizer additives and compositions to deliver micronutrient levels of trace metals to plants and for methods of producing such fertilizers with the required metal nutrients necessary for plant growth. The present invention solves those needs.